Introduction to Minitab for the Macintosh
- If you have no experience with Macintosh, please work
through the handout "Introduction to the Macintosh" before working through this
material.
- This handout includes instructions on saving and retrieving files from a
3.5" Macintosh diskette. You may want to have one available before
proceeding.
This introduction will cover the following topics:
Getting in and out of Minitab
We have to find the Minitab application icon, which looks like a fancy
arrowhead in a square. Once you find it, just double-click on it to launch
Minitab. Finding the Minitab application icon can be an adventure:
- In Sumwalt 311 or LeConte 127A, double-click on the hard-drive icon
(upper right of the desktop), then double-click on the folder entitled Minitab
or Minitab 8.2. The Minitab application icon should be somewhere in this
folder; you may need to scroll or expand the window.
- In LeConte 303A, double-click on the hard-drive icon, then double-click
on the applications folder. Then, double-click on the Minitab 8.2 folder. The
Minitab application icon should be somewhere in this folder.
- In the PSC Computing Lab, double-click on the "Apps" icon just below the
hard-drive icon. Then, double-click on the Macapps folder. In this window,
you will probably have to scroll down until you see the Minitab 8.2 folder.
Double-click on this. The Minitab application icon should be somewhere in this
folder.
If all else fails, the computer lab assistant should know where to find the
Minitab icon. After you find the icon and double-click on it, after a moment
you should see a window, the data window, named "untitled worksheet" and
a new set of menus across the top of the screen. You might notice another,
inactive, window behind the data window.
To exit minitab, select the item Quit from under the File menu. Close the Minitab folder and eject your diskette by dragging its icon to the trash.
Leave the Macintosh on.
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Inputting Data
For each student in an imaginary class, we have a name, an Exam 1 score,
and an Exam 2 score, shown in Table 1 below. We'll put their names in the
first column of the worksheet (C1), and Exam 1 and Exam 2 scores in the
second and third columns (C2, C3) of the worksheet. Rows of the
worksheet are called observations; columns are called variables.
When we do work on data, we can refer to variables by their column numbers C1,
C2 etc. or by more meaningful names we give them. Name the variables for
this data set:
- Click in the first empty box immediately under C1,
and type: Student.
Warning: do not type these variable names in the row labeled 1.
You'll have to retype the entire data set over again if you do.
- Hit the Tab button; this should move you one box to the right. Or, click
in that box.
- Type: Exam 1
- Tab again, or click in the next box to the right, and type: Exam
2
Table 1: Test scores for an imaginary class
| Student | Exam 1 | Exam 2 |
|---|
| Chakotay | 90 | 88 |
| Janeway | 90 | 98 |
| Kes | 76 | 81 |
| Kim | 88 | 64 |
| Neelix | 87 | 88 |
| Paris | 75 | 88 |
| Torres | 79 | 77 |
| Tuvok | 97 | 84 |
| Zimmerman | 71 | 79 |
Now, begin to input the data:
- Click in the first open box in column C1, under the word Student.
Type: Chakotay
- Tab to the next cell, and type: 90
- Tab to the next cell, and type: 88
Continue typing the names and test scores for all the students. If you make a
mistake, use the delete key, or click in the box containing the mistake and
retype the entry. If you get to the bottom of the data window, it should give
you more room automatically. Click on the arrows at upper and lower right of
the window to scroll through the window if it gets too large to see the whole
thing on the screen.
- Always double check data upon inputting it, as input errors are very common,
and if they are not corrected, all calculations will be in error, too.
- Sometimes after entering data, you will notice that some of the Minitab menu
items are in gray lettering, and that these items cannot be accessed. To
correct this, click in any empty cell of the worksheet. The menu items'
lettering should turn black again, and these items will become accessible.
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Modifying Data: An Example
Let's use Minitab to compute a mean score for each student. To
compute the average exam score by rows,
- Click-and-hold on the Calc menu.
- Keeping the mouse button depressed, move down the menu until the item
Functions and Statistics is highlighted; don't release the mouse.
Notice that another menu, a submenu, appears.
- Without letting the mouse button up, carefully move the pointer straight
to the right until it touches the submenu; if you slip, you'll have to go back
and try again.
- Move down this submenu until the item Row Statistics is
highlighted; then let the mouse button go, thereby selecting this item.
- In the newly opened window, at upper left is a box with a list of the
data set's numeric-variable columns (C2,C3) with their names. Click on
C2, then click in the box titled Select. Now repeat this for
C3. You have just selected these columns for the calculations (there
are several other ways to do this).
- At top right, you see a list with circles next to each item. Click in
the circle to the left of the word mean. You've just told Minitab that
you want to compute the mean of the selected columns C2 and C3
for each row.
- Click in the box next to the words Result in, and type the word:
mean. You've just given a name to the first open column of the
worksheet, C4, which will be used to store the results of the
calculation.
- Click the OK button.
You should soon see the worksheet, this time with a new column called
mean. In each row, the value of mean is the average of the student's
exam 1 and exam 2 scores.
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Sorting a Data Set
Now, if you were a teacher assigning grades, it would be easy for you to
see how the class as a whole did if the student records were sorted according
to the overall mean score. To sort the data set by this variable,
- Under the Calc menu, select the Sort item.
- Click-and-hold on C1, then drag down to C4; this should
highlight all four column names. Then click in the Select box. The
column names should appear in the Sort Columns box. You just selected
these four columns for the sort.
- Hit Tab. The blinking dash (the cursor) should now be in the
Put Into box. Select each of the columns C1-C4 again. They
should appear in the Put Into box.
- We want to sort according to the values in the mean column
(C4), so in the first line that says Sort by column, click in the
big box and type: C4 (or, type: mean).
- Since we want the sort to be from highest mean score to lowest, click
Descending next to the line where you just typed.
- Click OK.
After some delay, you should see the data window appear, but this time the
students are listed in order of greatest to least mean test score. What grades
would you give?
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Making a Stem-And-Leaf Plot
Minitab offers four possibilities to graphically describe a single
variable: the dotplot, the stem-and-leaf plot (or stemplot), the histogram,
and the boxplot. Hopefully, you have learned about these in a statistics
course, or soon will. The stemplot is especially good for small data sets. We
can make a stem-and-leaf plot using the following steps:
- Under the Graph menu, select the stem-and-leaf plot item.
- In the upper left of the newly-opened window, double-click on
mean. That word should now appear in the Variables window.
- Click OK.
The window which has been behind your data window all along, the Session
window, has now come to the front (become active). After a few seconds a
stem-and-leaf plot of the mean exam score data will appear there. Can you
figure out how to make other graphs, like the histogram or boxplot? The
procedure is very similar to the above.
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More About Minitab Windows
Minitab uses several different kinds of windows. To switch from one to
another, click anywhere in the window you want to activate, or select it's name
under the Windows menu.
- The Data window shows the worksheet in row-column form. From
here, you can create new variables, modify old ones, sort data, modify the
data, and much more.
- The Graph window will display certain graphs and plots (for
example, histograms and box plots). You may not have seen a Graph window yet,
but you will.
- The Session window will be valuable to us. If you can't see it,
activate it now. Besides the stem-and-leaf plot, there are other lines in
the window beginning with "MTB>" or "SUBC>". The fact is that every
action we've carried out by selecting menu items could also have been done by
entering commands in the Session window. Some types of work are much easier to
do this way. For example, click just to the right of the last MTB> line
(the Minitab prompt), and type: Print C1-C4 and push return.
The computer then prints the specified columns in the session window. Typing
commands in the Session window can be faster than selecting menu items. You
can even write entire Minitab programs, called macros.
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Printing a Window
Let's print the contents of the Session window. These instructions
assume you will be printing on an ImageWriter printer. If not, use your good
sense to modify them. If all else fails, the computer lab assistant should be
able to help you print.
- Make sure the Session window is active.
- Under the File menu, select Print Window.
- In the newly-opened dialog window, click in the circle next to the word
Faster. This mode is fast yet gives a better quality printout than the
Draft mode. Always use the Faster or Best mode when printing graphs.
- Click OK.
The printer for your group of Macintoshes should soon begin printing your
session window. It may be across the room, or even in the next room. When
it's finished (if it's an ImageWriter) carefully remove your output
from the printer like so:
- On the printer control panel, push the Select button.
- Push the form feed button.
- Push the Select button again.
- Gently tear off you hardcopy, without yanking on it.
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Saving and Retrieving Data
If you have a formatted Macintosh 3.5" diskette, insert it into the
internal disk drive. Save and name the worksheet to your diskette using
the following steps:
- Under the File menu, select the item Save Worksheet as.
- A box will open. Click the Drive button. You should see your
diskette's icon and name appear in the dialog box, meaning the data will be
saved to your diskette.
- Type a name for this worksheet: classdata
- Click the SAVE button.
There should now be a file on your minidisk with the name classdata.MTW.
To practice retrieving data from your diskette, first quit Minitab by selecting
the item Quit under the File menu. Close the Minitab folder and
eject your disk by dragging its icon to the trash.
To Open an Existing Minitab Worksheet
...if it is on your diskette:
- Insert your diskette into the internal disk drive.
- Double-click on your diskette's icon.
- The newly-opened window shows the contents of your diskette. There
should be an icon on your minidisk, labeled classdata.MTW. Double-click
on this icon to launch Minitab and open the classdata worksheet.
You should see the Minitab logo for a moment, then the classdata.MTWworksheet will open and you will see the data you entered above.
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